The effects of intracerebral inoculation of cerebrospinal fluid in mice from 9 patients with amyotrophic lateral sclerosis are reported. There were 704 animals inoculated. The results were considered positives when the animals presented difficults in walking and equilibrating. Cases 1, 2, 6, 7 and 9 were positives in first passage. In case 1, the positivity was reached from first to fourth passage and in case 6. to third passage. At sight of this results, the possibility of that disease to be caused by slow-virus is discussed.